Dibenzylidene sorbitol acetals (“DBS”), substituted DBS, such as can be made with alkyl substituted aromatic aldehydes, and related acetals have found utility as nucleating agents, clarifying agents, gelling agents, processing aids, and strength modifiers in polyolefin resins, polyester resins, deodorant, and antiperspirant compositions; hydrocarbon fuels; waste liquids, especially those containing organic impurities; and paint.
Such compounds are utilized to provide nucleation sites for polyolefin crystal growth during cooling of a molten formulation. Without being limited to one specific scientific theory, it is believed that DBS compounds form fibrous networks within the molten polyolefin (such as polypropylene) at a temperature well above that required for polyolefin crystal formation. The fibrous networks appear to act as sites for more ordered and faster polyolefin crystallization during cooling. During the process of crystallization, polymer crystals organize into larger superstructures which are referred to as spherulites. The more uniform, and preferably smaller, the spherulite size, the reduced possibility for light to be scattered. In such a manner, optical opacity of the polyolefin article itself can be controlled. Thus, DBS compounds are very important to the polyolefin industry in order to provide such desired nucleation and clarification properties.
DBS derivative compounds are typically prepared by the condensation reaction of two moles of an aromatic aldehyde with one mole of a polyhydric alcohol, such as xylitol or sorbitol. Examples of suitable processes may be found in Murai et al., U.S. Pat. No. 3,721,682; Murai et al., U.S. Pat. No. 4,429,140; Machell, U.S. Pat. No. 4,562,265; Kobayashi et al., U.S. Pat. No. 4,902,807; and Scrivens et al., U.S. Pat. No. 5,731,474. All of these references are hereby incorporated by reference in their entirety.
Specific clarifying and nucleating agents for polyolefins include bis-3,4-dimethyldibenzylidene sorbitol (3,4-DMDBS) and bis-p-methyldibenzylidene sorbitol (MDBS). These specific compounds and polyolefins containing such compounds have been taught previously in U.S. Pat. No. 4,371,645 to Mahaffey and U.S. Pat. No. 5,049,605 to Rekers, respectively. Such compounds are thus individually well known as polyolefin additives and exhibit excellent low haze measurements within polyolefins (as low as about 8.0% for 3,4-DMDBS and about 10% for MDBS in random polypropylene copolymer injection molded 50 mil thick plaques having 2000 ppm of clarifier added).
However, there are drawbacks from utilizing MDBS as a clarifying agent since degradation of such a compound into the benzaldehyde and sorbitol components creates a problem with migration of such benzaldehydes from the target polyolefin. In such a situation, foul odors and tastes are generated such that the target polyolefin is limited in its end-use function to non-food contact applications. To combat this, Milliken & Company developed 3,4-DMDBS. Such a compound appears to suffer from the same type of degradation possibilities; however, the resultant benzaldehyde, being 3,4-dimethyl substituted, does not create the same organoleptic problems as its p-methylbenzaldehyde counterpart. As a result, 3,4-DMDBS has become the primary clarifying agent throughout the polyolefin market.
Unfortunately, though, 3,4-DMDBS is relatively expensive to manufacture. The manufacturing costs required to produce 3,4-DMDBS are above those for MDBS. As a result, there remains a great desire to develop a more cost-effective, yet acceptable clarifying agent or composition for polyolefins which exhibits similar haze results as either of the two compounds individually. To date, there has been no teaching or fair suggestion for any such improvements to lower the amount of 3,4-DMDBS in order to reduce the costs of such a composition solely comprising such a polyolefin clarifying agent without sacrificing clarification ability. There does exist a combination of 3,4-DMDBS with bis(p-chlorobenzylidene) sorbitol in Japanese Application Hei 8[1996]-199003 to Kobayashi; however, such a composition provides deleterious results from an organoleptic perspective. Japanese Application Hei 8[1996]-32415, also to Kobayashi, teaches a combination of MDBS with bis-p-chlorodibenzylidene sorbitol as a polyolefin additive as well. Again, organoleptics are problematic with such a composition. Neither teaching shows or fairly suggests the combination of 3,4-DMDBS and MDBS. The only other teachings concerning such polyolefin clarifying compounds have been as individually utilized compounds within polyolefin compositions and articles, as noted above. Thus, there remains a desire to provide a more cost-effective but similarly performing clarifying agent comprising the excellent clarifier 3,4-DMDBS.